Since optical elements used in slimming devices such as organic electroluminescence (organic EL) illumination devices or liquid crystal display devices are required to have high light transmission, transparency and stiffness, a glass substrate is employed as a substrate for optical elements. However, such a glass substrate is fragile, as well as is not easy to manufacture and handle it. As more miniaturization, slimming, lightweight and further flexibility are required for such optical devices, a transparent and flexible resin film may be usefully used instead of a glass substrate because the resin film is capable of winding as a roll, is easy to handle, is efficiently manufactured, has an improved design properties, and is inexpensive.
Meanwhile, since resin films transmit gas such as water vapor, for optical elements using a resin substrate instead of a glass substrate, water vapor transmitting the resin substrate permeates the interior of optical elements, resulting in degrading optical elements. Specifically, for organic EL illumination devices using an organic EL element in which a light-emitting membrane comprising organic EL is formed on a resin substrate, the organic EL is reacted with electrode components in the presence of water and converted into a material little involvement in light-emitting. As a result, parts without emitting light, i.e., so-called dark spots appear as stains on a surface light source, resulting in lowering illumination quality.
Also, for liquid crystal display devices having a liquid crystal panel using a polarizer plate which equips a polarizing film on a resin substrate, as viewed in an oblique direction (oblique sight), contrast deterioration or color mismatching (chromaticity mismatching) by light-leak phenomena is caused. This condition is more significant under high temperature and high moisture. This is attributable to the following reasons: for example, decomposing a complex of polyvinylalcohol (PVA) and iodine constituting a polarizer contained in a polarizing film by water transmitting a resin substrate or permeating a side of the resin substrate; altering optical anisotropy of a polarizing film by a dimensional change due to absorption and discharge of water; or deteriorating functionality of an optical compensation plate provided between a substrate and a polarizing film to enlarge a viewing angle and further producing cracks in the optical compensation plate. Examples of complexes used as a polarizer may include I5-PVA complexes which exhibit a peak around 600 nm, a broad absorption band, red color upon decomposition, and easy decomposition under high temperature and high moisture; I3-PVA complexes which exhibit a peak around 480 nm, a broad absorption band, and blue color upon decomposition; or the like.
In the field of resin substrates used in such optical elements, substrates having improved gas barrier properties are being developed. Specifically, for organic EL elements, there have been reported an organic EL element in which a silicone oxide nitride is provided on a film such as a polyester film (Patent document 1); an organic EL element using a gas-barrier film which has a stress-relief layer such as polysilazane having a particular thermal expansion coefficient and a gas-barrier layer such as silica on a film such as polyethyleneterephtalate (Patent document 2); an element body such as an organic EL element having function to transfer permeated water to the other side of element side by using a resin substrate having an inorganic layer such as silicon nitride and an organic film layer comprising a lower contact angle layer and a higher contact angle layer(Patent document 3).
Further, it has been reported a polarizer plate for liquid crystal display devices having improved gas-barrier properties, manufactured by forming a layer of silicon oxide having a particular contact angle on a transparent substrate film and laminating a polarizing element thereon (Patent document 4).
However, in case of conventional transparent substrates for optical elements, cracks may be easily generated in an inorganic layer comprising silicon oxide or the like formed on a resin film of a substrate and further stripping may be caused. As a result, gas-barrier properties are lowered. Thus, there is a need for a transparent substrate for optical elements which is capable of inhibiting water vapor permeation through a resin substrate sufficiently.